1. Field of the Invention
The present invention relates to a digital video/audio recording and reproducing apparatus for compressing and encoding digitized video and audio signals, recording the thus encoded data on a recording medium such as a magnetic tape, and reproducing the data recorded on the recording medium.
2. Description of Related Art
It is known to provide a digital video/audio recording and reproducing apparatus for digitizing video and audio signals simultaneously, recording the digitized signals on a recording medium such as a magnetic tape, magnetic disk, or optical disk, and reproducing simultaneously both the video and audio signals recorded on the recording medium for conversion into an analog representation. FIG. 1 is a block diagram showing the configuration of such a known digital video/audio recording and reproducing apparatus, disclosed in the July 1988 issue of Hosho Gijutsu (Broadcast Technology).
In FIG. 1, the numerals 1 and 2 designate a video A/D converter and an audio A/D converter, respectively, for converting an input analog video signal and an input four-channel channel analog audio signal into a digital representation. The video signal digitized by the video A/D converter 1 is supplied to a C2 encoder 3, which derives a C2 parity in the error-correction encoding of the video signal, appends it to the video signal, and delivers the video signal with the C2 parity to an interleave 4 where the video signal is shuffled. The audio signal digitized by the audio A/D converter 2 is supplied to an audio error-correction encoder 5 where the digitized audio signal is error-correction encoded. The video signal shuffled in the interleave 4 and the audio signal error-correction encoded by the audio error-correction encoder 5 are combined in an adder and delivered to a C1 encoder 6. The C1 encoder 6 derives a C1 parity for the combined data, appends it to the data, and delivers the data with the C1 parity to a modulator 7 where the error-correction encoded data is encoded for recording. The data encoded for recording is recorded on a magnetic tape 8 by means of a magnetic head 10 mounted on a rotating drum 9.
The reference numerals 11 to 19 indicate components comprising a reproduction system, wherein the numeral 11 designates a demodulator for decoding the replay data played back from the magnetic tape 8. The data thus decoded is directed to a C1 decoder 12 which performs error correction based on the C1 parity word and delivers the error-corrected replay data to an A/V separation circuit 13. The A/V separation circuit 13 separates the replay data into a video signal and an audio signal and supplies the video signal to a deinterleave 14 and the audio signal to an audio error-correction decoder 18. The deinterleave 14 deshuffles the supplied video signal and delivers the deshuffled video signal to a C2 decoder 15 which performs error-correction based on the C2 parity word and delivers the error corrected video signal to an interpolation circuit 16. The interpolation circuit 16 performs interpolation on the video signal if there are any uncorrectable errors, and after processing, delivers the video signal to a video D/A converter 17 which converts the digital video signal into an analog signal for output. The audio error-correction decoder 18 performs error-correction on the supplied audio signal and delivers the error-corrected audio signal to an audio D/A converter 19 which converts the digital audio signal into an analog signal for output.
The operation of the above apparatus will now be described.
The input analog video signal is converted into a digital signal by the video A/D converter 1, and the digitized video signal is supplied to the C2 encoder 3 which appends the C2 parity for error correction. The video signal with the C2 parity is read into the interleave 4 where prescribed shuffling is performed on the video signal, after which the video signal is fed to the adder. On the other hand, the input analog audio signal is digitized by the A/D converter 2 and error-correction encoded by the audio error-correction encoder 5, after which the audio signal is fed to the adder where it is combined with the video signal. The combined data is fed to the C1 encoder 6 where the C1 parity is appended. The shuffled and error-correction encoded data is supplied to the modulator 7 which encodes it for recording. The data is now recorded on the magnetic tape 8 by means of the magnetic head 10. FIG. 2 shows the signal recording format recorded on the magnetic tape 8. The video signal and the four-channel audio signal are recorded in different areas on the same track, the audio signal being recorded outwardly of the ends of the video signal.
In the reproduction system, the digital data played back by the magnetic head 10 is fed to the demodulator 11 for decoding, after which the C1 decoder 12 performs error correction based on the C1 parity word. The output data from the C1 decoder 12 is separated into a video signal and an audio signal by the A/V separation circuit 13. The audio signal is processed by the audio error-correction decoder 18 and then converted by the audio D/A converter into a four-channel analog signal for sound reproduction. On the other hand, the video signal is deshuffled by the deinterleave 14 to rearrange it into the original order, after which the C2 decoder 15 performs error correction based on the C2 parity word; if there are any uncorrectable errors, error flags are attached, and the interpolation circuit 16 performs one-dimensional or two-dimensional interpolation on the video signal, the thus processed video signal then being converted by the video D/A converter 17 into an analog video signal for picture reproduction.
However, the conventional digital video/audio recording and reproducing apparatus having the above construction has the disadvantage that in order to reduce the overall size of the apparatus, if the size of the recording medium (magnetic tape) is made smaller, a shorter recording time will have to be tolerated, and if the size of the magnetic head is reduced, the recording data transfer rate (information amount) will drop, resulting in degradation in both the picture and the sound quality.
Furthermore, because of the fixed structure of the video signal recording areas and the audio signal recording areas on the recording medium (magnetic tape), as shown in FIG. 2, the maximum number of recordable audio signal channels is determined by the recording format, which gives rise to the problem that the number of audio signal channels cannot be increased beyond the predetermined maximum number; therefore, a digital video/audio recording and reproducing apparatus designed for two-channel audio recording, for example, cannot be used for recording three or more audio signal channels by using the same recording format.
Generally, in magnetic tape recording using a rotating magnetic head, the reproduction signal quality obtained from the ends of the recording tracks is inferior to that obtained from the center thereof, since errors frequently occur in the reproduction signal from the ends of the tracks. Presumably, this is because the magnetic head to magnetic tape contact characteristic is unstable at the ends of the recording tracks compared to the center thereof. In digital recording and reproducing apparatus for business use, since the recording density is set at a relatively low rate to maintain reliability, the signal quality acceptable for practical use can be obtained even from the ends of the recording tracks. However, the recording format having audio signals recorded at the ends of the tracks as shown in FIG. 2, when applied to a digital video/audio recording and reproducing apparatus designed for a higher recording density, gives rise to the problem that there occurs degradation in the sound quality since the signal quality degrades at the ends of the tracks. On the other hand, in a recording format in which the video signal recording areas are disposed at the ends of the recording tracks, degradation in the picture quality will result. Thus, the degradation of the reproduction signal quality at the ends of the tracks has the problem of causing errors in the reproduced video or audio signals.